Use of the present invention shall be described throughout the specification in relation to adjusting the length of the shaft of sporting implements—for example paddles used to propel watercraft such as standup paddle boards or kayaks and tool bits—for example a screwdriver bit. However, it should be appreciated that the present invention can be used in other applications in which objects—particularly those having shafts—are to be connected to each other, and the exemplary embodiments are not intended to be limiting.
In the context of standup paddle boards, the optimal length of a paddle may vary between individuals based on their physical characteristics, or paddling styles. Further, an individual may want to adjust the length of a paddle to account for changes in paddling style—whether to account for current weather conditions, fatigue levels, or the current activity (for example racing versus recreational paddling).
Numerous mechanisms have been used to provide adjustability in paddles—for example, spring pin arrangements, pressure cleats, and clamps. US Patent Application Publication No. 2012/0028518 describes a system wherein a lever on the paddle handle is used to release and activate a plug on a lower shaft portion.
However, such systems have inherent flaws—for example being visually or physically obtrusive on the exterior of the paddle shaft, mechanically complicated, or using metal parts which rust over time.
Another type of adjustment mechanism is described in New Zealand Patent No. 551189. The mechanism includes a shaft to which a helical wire spring is attached. The shaft and springs fits within an external sleeve.
In use, the spring biases against the internal surface of the external sleeve to cause a friction fit. To move the external sleeve with respect to the shaft, a tool is passed through the sleeve to connect with the spring. The spring is then twisted causing the circumference of the spring to lessen, thus disengaging the spring from the internal surface of the sleeve. This enables the sleeve to be moved with respect to the shaft. Upon release of the spring, the material memory of the spring causes it to revert to its original larger circumference and press against the sleeve.
US Patent Application Publication No. 2011/0306438 describes a connector based on a similar principle, although reversed—with the helical spring biased inwardly against the external surface of a shaft positioned within it.
While the connectors act as effective adjustment mechanisms in certain applications, there remains room for improvement. In particular, under certain load conditions the helix can misbehave when moving beyond a desired range, leading to negative effects such as failure of the friction fit allowing the shafts to slip relative to each other, shifting of the connector as the helix settles on release, or damaging the helix itself.
Additionally, its been observed that in some circumstances, the helix may expand differently along its length—leaving portions of the helix engaged while others are disengaged.
Aspects of misbehaviour may be compensated for to a degree by increasing the strength of the spring, but this can make adjustment more difficult, and the parts heavier and more costly. Further, some aspects of misbehaviour may remain uncorrected by simply changing characteristics of the spring.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
All references, including any patents or patent applications, cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the reference states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms parts of the common general knowledge in the art, in New Zealand or in any other country.
Throughout this specification, the word “comprise”, or variations thereof such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.